Multiple beam antennas are antennas that form a plurality of communication beams. Commercial communications satellites typically employ multiple beam antennas that have one or more feed elements. The feed elements may be direct radiating or they may feed a reflector or a lens.
Multiple beam antennas have feed element groups that overlap, whereby a feed element is driven to generate a beam component that is combined with component beams from other feed elements to form a composite beam, or communications beam. A low-level beam forming network within the communications satellite controls the interaction of feed elements.
Conventional beam forming networks that generate multiple beams from a feed array describe planar dividers and combiners connected by individual connections having predetermined propagation delays. The beam forming networks are typically comprised of seven-way power dividers and combiners. The excessive number of divider and combiner structures required in these prior art beam forming networks are large and adversely affect signal routing design efficiency.
An example of a prior art beam forming network power divider 100 is shown in FIG. 1. An input signal is divided seven ways. Each element 103 receives a main vector 102 and six coupled vectors 104 surrounding the main vector 102. Each signal vector 102, 104 is weighted in amplitude and phase before combining in a power combiner 200 shown in FIG. 2. Inputs 202 from six of the adjacent elements 103 are combined to produce a single output. Typically, the power divider network is on a separate section from the power combiner network.
The prior art beam forming networks require divider and combiner networks, like the ones shown in FIGS. 1 and 2, that send and receive signal energy from all adjacent cells in two polarizations. For a hexagonal structure, a center cell surrounded by six cells, the dividing network is 1:7 and is repeated for all cells and all polarizations. Undesirable interference occurs between adjacent cells. The seven-way power divider and combiner networks are unnecessarily complex adding unwanted size and weight to the beam-forming network.